Optoelectronic method and appliance for measuring the inside diameter of a hollow body

ABSTRACT

The invention relates to a method of measuring the inside diameter of a hollow body ( 2 ). According to the invention:
         the hollow body ( 2 ) is illuminated from one side by a diffuse light source ( 9 ) presenting two light boundaries ( 9   1   , 9   2 ) that are spaced apart along the measurement axis (x) so as to create two light transitions in an image, which transitions are spaced apart from each other and diametrically opposite;   from the side of the hollow body that is opposite from its illuminated side, the light rays that are reflected and refracted by the hollow body ( 2 ) are recovered to form at least one image in which there appear at least the two light transitions; and   the image is processed in order to determine the distance between the two light transitions in order to determine a measurement for the inside diameter of the hollow body.

The present invention relates to the technical field ofoptoelectronically inspecting hollow items or containers in a generalsense, and that are of a transparent or translucent nature, such as forexample glass bottles, pots, or jars, in order to inspect or evaluatedimensional characteristics presented by such a hollow item.

A particularly advantageous but non-exclusive application of theinvention lies in measuring the inside diameter of a hollow body, and inparticular the inside diameter of the neck of a bottle.

In this field of application, there is a need to measure the insidediameter of a hollow item in order to determine whether the hollow itemcomplies with dimensional criteria. For example, in the field of glassbottles, the inside diameter of the neck of a bottle must be measured inorder to determine whether this portion of the bottle complies withcriteria for ensuring that the bottle will be corked and uncorkedcorrectly by a cork subsequently inserted into the neck of the bottle.

Various techniques are known for measuring the inside diameter of theneck of a container. For example, it is known to place a diffuse lightsource under the bottom of a container and to place a camera above itsneck, the camera having a telecentric lens enabling the neck to beobserved along its axis of revolution. It is thus possible to form animage of the neck of the container in which there can be seen a paledisk in the center of the image representing the smallest throughsection in the neck. That inspection technique makes it possible tomeasure the smallest diameter of the neck of the container regardless ofits position along the neck of the container. That technique thereforedoes not make it possible to measure the inside diameter of the neck ata determined height along its vertical axis of revolution, thus puttinga limit on the dimensions of the containers that can be inspected. Inorder to fully inspect corking and uncorking conditions of a container,it is necessary to be able to measure the inside diameter of the neck atleast one determined section of the neck that is different from thesection corresponding to its smallest diameter.

US patent application No. 2008/0198389 discloses an appliance formeasuring the inside and outside diameters of a transparent tube. Thatappliance uses a collimated laser beam to illuminate the transparenttube along a line of light that is inclined relative to a planeperpendicular to the longitudinal axis of the tube. The light that isintercepted and refracted by the transparent tube is recovered by acamera via a screen that is interposed between the tube and the camera.Analyzing the shape of the recovered light beam makes it possible todetermine the inside diameter along the transparent tube.

Such an appliance does not make it possible directly to measure theinside diameter of a hollow body at different sections of the hollowbody. In an image, it is only the diameter at the level of the lightsource in the form of a line that can be measured. It is thereforenecessary to cause the tube and the sensor to move relative to eachother in a direction parallel to the central axis of the tube in orderto make other measurements in other cross-sections, where this movementis in addition to rotating the item about its axis.

Patent applications JP 57 142505 and JP 11 132730 also describe a methodof measuring the inside diameter of a tube with the help of a light beampassing through the tube and recovered by an electronic detectorcircuit. Such methods do not make it possible to detect accurately theinside diameter of a hollow body. Those methods require scanning bymeans of a source of finely collimated light of the laser type. The itemmust be held stationary so that it has no degree of freedom of movementin said transverse direction, at least throughout the complete scan ofits entire cross-section, and that is not suitable for rapid industrialinspection of items that are heavy and imperfect. Furthermore, measuringa plurality of diameters on the same section requires the article to berotated about its own axis, using rotation in increments with a stop ateach increment, thereby occupying a large amount of time for analysis.Furthermore, if it is also desired to measure diameters at a pluralityof cross-sections, measurement time becomes completely prohibitive, orelse there are major errors due to the item moving while measurement isbeing performed.

The invention thus seeks to remedy the drawbacks of the prior art byproposing a technique that is simple to perform and that makes itpossible in an industrial environment to measure rapidly and with greataccuracy at least the inside diameter(s) of a hollow body at any heightalong the axis of revolution of the hollow body.

To achieve such an object, the method of the invention seeks to measurethe inside diameter of a hollow body of revolution that is transparentor translucent and that is defined by an inside face and an outsideface, the body presenting an axis of revolution along a vertical axis,the method consisting in illuminating the hollow body by means of adiffuse light source and in recovering the light rays emerging from thehollow body in order to form at least one image. According to theinvention, the following steps are performed:

-   -   illuminating the hollow body on one side by means of a diffuse        light source so that the incident light rays pass through the        hollow body along at least one cross-section perpendicular to        the axis of revolution and in which the inside diameter is to be        measured along a measurement axis, the light source presenting        two light boundaries spaced apart along the measurement axis so        as to create two light transitions in the image that are spaced        apart from each other and diametrically opposite about the        vertical axis, corresponding to emerging light rays that        propagate along respective lines tangential to the inside face        and perpendicular to the diameter;    -   from the side of the hollow body that is opposite from its        illuminated side, and by acting along an optical axis that is        perpendicular to the vertical axis and perpendicular to the        measurement axis, recovering the light rays that are reflected        and refracted by the hollow body so as to form at least one        image in which there appear at least the two light transitions;        and    -   processing the image so as to determine the distance along the        measurement axis between the two light transitions in order to        determine a measurement for the inside diameter of the hollow        body.

The invention also seeks to propose a method making it possible todetermine the inside diameter of a hollow body at different positionsalong the axis of revolution of the hollow body.

To achieve such an object, the method consists in illuminating a regionof the hollow body that extends over a determined height along thevertical axis, in recovering the reflected and refracted emerging lightrays so as to form an image of the hollow body over said height, and indetermining the distance along the measurement axis between two lighttransitions at different levels along the vertical axis so as todetermine measurements for the inside diameter at different heights ofthe hollow body.

In addition, the method of the invention may also present in combinationat least one and/or another of the following additional characteristics:

-   -   causing the hollow body to rotate about the axis of revolution        through at least part of a revolution and processing the images        for different angular positions in rotation of the hollow item,        with a measurement for the inside diameter at one or more        heights being taken in each of those images;    -   determining the profile of the inside face from inside diameter        measurements taken at different heights;    -   comparing the measurements of the inside diameter with reference        values in order to determine whether the hollow body is or is        not defective;    -   illuminating the hollow body by a light source having light        boundaries on either side of the optical axis that lie along the        measurement axis strictly between the position of an internal        incident light ray and the position of an external incident        light ray, the internal incident light ray generating the        emerging light ray that is only refracted on passing through the        hollow body and that is situated farthest from the optical axis,        while the external incident light ray generates the emerging        light ray that is reflected by the inside face of the hollow        body and that is the closest to the optical axis;    -   illuminating the hollow body by a light source that emits light        from its center and up to its light boundaries; and    -   illuminating the hollow body by a light source that extends from        the two light boundaries on either side of the axis and beyond        the external incident light ray.

The invention also seeks to propose an appliance for measuring theinside diameter of a hollow body of revolution that is transparent ortranslucent.

To achieve such an object, the appliance for measuring the insidediameter of a hollow body of revolution that is transparent ortranslucent and that is defined by an inside face and an outside facepresents an axis of revolution along a vertical axis, the appliancecomprising a light source emitting light rays illuminating the hollowbody and a recovery system for recovering light rays emerging from thehollow body in order to form at least one image, and an imageacquisition and processor unit. According to the invention, theappliance comprises:

-   -   a diffuse and extensive light source arranged so that the        incident light rays pass through the hollow body from one side        and along at least one cross-section perpendicular to the axis        of revolution and in which the inside diameter is to be measured        along a measurement axis, the light source presenting two light        boundaries spaced apart along the measurement axis so as to        create two light transitions in the image, which transitions are        spaced apart from each other and diametrically opposite about        the vertical axis, corresponding to emerging light rays that        propagate along respective lines tangential to the inside face        and perpendicular to the diameter;    -   on the side of the hollow item opposite from its side        illuminated by the source, a recovery system for acting along an        optical axis that is perpendicular to the vertical axis and        perpendicular to the measurement axis to recover emerging light        rays as reflected and refracted by the hollow item, the system        forming at least one image in which there appear at least two        light transitions that are spaced apart from each other and        diametrically opposite relative to the vertical axis; and    -   an image acquisition and processor unit formed by the recovery        system in order to determine the distance along the measurement        axis between the two light transitions in order to determine a        measurement for the inside diameter of the hollow body.

In addition, the appliance of the invention may also present incombination at least one and/or another of the following additionalcharacteristics:

-   -   the diffuse and extensive light source possesses a determined        height along the vertical axis for illuminating a vertical        region of the hollow body, the recovery system recovers the        emerging light rays reflected and refracted by the hollow body        in a vertical region in order to form a corresponding image, and        the image processor unit determines the distance between two        light transitions along the measurement axis at different levels        along the vertical axis in order to determine measurements for        the inside diameter at different heights of the hollow body;    -   a system for causing the hollow body to rotate about the axis of        revolution;    -   the light boundaries of the light source on either side of the        optical axis lie along the measurement axis strictly between the        position of an internal incident light ray and the position of        an external incident light ray, the internal incident light ray        generating the emerging light ray that is only refracted on        passing through the hollow body and that is situated farthest        from the optical axis, while the external incident light ray        generates the emerging light ray that is reflected by the inside        face of the hollow body and that is the closest to the optical        axis;    -   the source is luminous from its center out to its light        boundaries forming its vertical edges;    -   the light boundaries of the light source are optionally        rectilinear with a profile that is adapted to the profile of the        inside diameter of the hollow body;    -   the light source includes an adjustment system serving to vary        the distance between the light boundaries;    -   the adjustment system comprises one or more masks for the light        source, or a light source made using a series of light-emitting        diodes with on/off control; and    -   the recovery system comprises a camera having a telecentric lens        so that the collected emerging light rays are parallel to the        optical axis of the recovery system.

Various other characteristics appear from the following description madewith reference to the accompanying drawings, which show embodiments ofthe invention as non-limiting examples.

FIG. 1 is an elevation view showing an embodiment of an appliancemeasuring the inside diameter of a hollow body.

FIG. 2 is a plan view of the measurement appliance shown in FIG. 1.

FIG. 3 is an example of an image taken of a hollow body and enabling itsinside diameter to be measured.

As can be seen more clearly in FIGS. 1 and 2, the invention relates toan appliance 1 for measuring the inside diameter of a hollow body 2 thatis transparent or translucent. In the example shown, the hollow body 2is a container having an axis of revolution that is the vertical axis z.The hollow body 2 thus has a wall 3 that is defined by an inside face 4and an outside face 5. In the preferred embodiment shown of a hollowitem 2 such as a bottle, the hollow body 2 has a neck 6 in which atleast one inside diameter D_(j) of the hollow body 2 is to be measured.The inside diameter of the hollow body 2 is taken between two points ofthe inside face 4 that are situated on either side of the vertical axisz. Thus, the inside diameter is measured along a measurement axis x thatis perpendicular to the vertical axis z (FIG. 3).

The appliance 1 also has a light source 9 of diffuse and extensivenature that emits incident light rays I_(i) as shown in FIG. 2. Thediffuse nature of the light source 9 should be understood in theconventional sense used in optics, i.e. each point of the light source 9emits light in a multitude of directions. An emitting surface of theLambertian type is a perfect model of this type of source, but naturallythe range of angles emitted by the source could be restricted and theemission lobes need not be exactly hemispherical. The light source 9 isarranged on one side of the item 2 so that an incident light ray I_(i)passes through the hollow body 2 along at least one cross-section S_(j)perpendicular to the vertical axis z and in which the inside diameterD_(j) is measured along the measurement axis x.

The appliance 1 also has a recovery system 11 acting on an optical axisy perpendicular to the vertical axis z and perpendicular to themeasurement axis x, for recovering emerging light rays E_(i) asreflected and refracted by the hollow body 2 from its side opposite fromits side that is illuminated by the light source 9. As can be seenclearly in FIGS. 1 and 2, the light source 9 and the recovery system 11are thus arranged on either side of the hollow body 2.

By way of example, the light beam recovery system 11 may comprise acamera 12 fitted with a lens 13 suitable for forming images. The camera12 is connected to an image acquisition and processor unit 15 that isadapted to analyze the video signal delivered by the camera, inparticular in order to measure the inside diameter of the hollow bodyfrom the images taken.

In a preferred embodiment, the camera 12 is provided with a telecentriclens 13 so that the emerging light rays E_(i) that are collected areparallel to the optical axis y of the recovery system 11.

In an advantageous variant embodiment, the inspection zone of the camera12 extends over a determined height along the vertical axis z of thehollow body in which it is possible to determine the inside diameter atvarious levels taken perpendicularly to the vertical axis z. For thisthe light source 9 presents a height Z_(L) along the vertical axis z. Inthis variant embodiment, the light source extends firstly along themeasurement axis x in order to present two light boundaries 9 ₁ and 9 ₂,and secondly along the vertical axis x, over a height Z_(L).

In accordance with the invention, the light source 9 presents first andsecond light boundaries 9 ₁, 9 ₂ that extend vertically, i.e. in theexample shown in a straight direction parallel to the vertical axis z.These two light boundaries 9 ₁ and 9 ₂ are spaced apart from each otheralong the measurement axis x. In the example shown in FIGS. 1 and 2,these light boundaries 9 ₁ and 9 ₂ correspond to the vertical edges ofthe light source 9. In this variant, the source 9 is luminous from itscenter and out as far as its two vertical edges 9 ₁, 9 ₂. In otherwords, the light source 9 does not emit light beyond the vertical edges9 ₁, 9 ₂, such that these edges constitute light boundaries. In otherwords, each light boundary 9 ₁ and 9 ₂ corresponds to the junction zonealong the measurement axis x between a light-emitting zone and a zonethat does not emit light.

The light source 9 presents first and second light boundaries 9 ₁ and 9₂ so as to create, in the image formed by the camera 12, respectivefirst and second light transitions T₁, T₂ that are spaced apart fromeach other and diametrically opposite about the vertical axis z, andthat correspond to the emerging light rays that propagate tangentiallyto the inside face 4 and perpendicularly to the diameter of the hollowbody. With reference to the notion of light boundaries 9 ₁ and 9 ₂, alight transition T₁, T₂ observable in an image J corresponds to adifference in gray level, such as for example changing from a pale zoneto a dark zone, or vice versa.

The camera 12 thus recovers the emerging light rays E_(i) that have beenreflected and refracted by the hollow item 2 from the side opposite tothe side that is illuminated by the light source 9. The recovery system11 thus forms at least one image J (FIG. 3) in which there can be seenat least the two light transitions T₁ and T₂ that are spaced apart fromeach other and that are diametrically opposite about the vertical axisz.

As can be seen more clearly in FIG. 3, the resulting image J isprocessed by the acquisition and processor unit 15 so as to determinethe distance along the measurement axis x between the two lighttransitions T₁ and T₂ in order to determine a measurement of the insidediameter D_(j) of the hollow body 2.

According to a characteristic of the invention, the light boundaries 9 ₁and 9 ₂ lie strictly along the measurement axis x between the positionof an internal limiting incident light ray I₃ and the position of anexternal limiting incident light ray I₄ (FIG. 2). The positions of thelimiting incident light rays are defined as follows.

The light source 9 is such that the two light boundaries 9 ₁ and 9 ₂ lieon either side of the optical axis y of the recovery system 11. Forsimplification purposes, the description below seeks to describe solelythe position of the first light boundary 9 ₁. It should thus be observedthat only incident light rays I₁, I₂, I₃, and I₅ situated between theoptical axis y and the first light boundary 9 ₁ of the source 9 areshown in FIG. 2. Naturally, the paths followed by the light rays fromthe source 9 are symmetrical on either side of the optical axis y, suchthat the position of the second light boundary 9 ₂ is definedidentically to the corresponding position of the first boundary 9 ₁.

It should be considered that the incident light rays I₁ and I₂ are onlyrefracted on passing through the hollow body 2, such that thecorresponding emerging light rays E₁, E₂ are picked up by the camera 12so that a pale zone appears on the image (FIG. 3).

The incident light ray I₃ passes through the hollow body 2 while beingonly refracted on passing through the body 2. To this end, the emerginglight ray E₃ corresponds to that one of the light rays collected by thecamera 12 and that are only refracted on passing through the hollow body2 that is the farthest from the optical axis y. The emerging light rayE₃ is such that it propagates along a line tangential to the inside face4 and perpendicular to the diameter. As can be seen more clearly in FIG.2, the line on which the emerging light ray E₃ propagates is tangentialto the inside face 4 at a point P. It should be considered that theincident light ray I₃ is the “internal” limiting incident light ray forwhich a pale zone appears in the image J. The internal limiting incidentlight ray I₃ generates the emerging light ray E₃ that is only refractedon passing through the hollow body 2 and that is situated farthest fromthe optical axis y. In other words, the internal limiting incident lightray I₃ corresponds to the transition between refraction and reflectionfor the emerging light rays, thereby leading to the creation of thelight transition T₁ in the image J.

FIG. 2 shows an incident light ray I₄ that is farther away from theoptical axis y than is the incident light ray I₃. The incident light rayI₄ penetrates into the wall of the hollow body 2, is reflected on itsinside face 4, and is then refracted on exiting through the outside face5 so as to give rise to an emerging light ray E₄. It should be observedthat the path followed by the emerging light ray E₄ is tangential to theinside face 4 of the hollow body at a point P. In other words, theemerging light rays E₃ and E₄ both coincide with the direction that istangential to a common point P on the inside face 4 of the hollow body2.

It should thus be considered that the emerging light ray E₄ is that oneof the emerging light rays collected by the camera 12 and that have beensubjected to reflection on the inside face 4 on passing through thehollow body 2 that is the closest to the optical axis y. Thus, if thelight source 9 emits the incident light ray I₄, that masks the lighttransition T₁ in the image J. In order to avoid this phenomenon, thelight boundary 9 ₁ is such that the light source 9 does not generate theincident light ray I₄. The incident light ray I₄ is thus the externallimiting incident light ray for positioning the light boundary 9 ₁. Theexternal limiting incident light ray I₄ corresponds to the light raythat generates that one of the emerging light rays reflected by theinside face 4 of the hollow body that is the closest to the optical axisy.

In other words, the first light boundary 9 ₁ must be situated relativeto the optical axis y so as to be set back relative to the externallimiting light ray I₄. Under such conditions, a dark zone appears in theimage J corresponding to the light transition T₁. It should beconsidered that the closer the first light boundary 9 ₁ to the externalincident light ray I₄, the smaller the width of the dark zone or lighttransition T₁. By way of illustration in FIG. 2, an incident light rayI₅ is shown close to the first light boundary 9 ₁. This incident lightray I₅, which is situated between the incident light rays I₃ and I₄,gives rise to an emerging light ray E₅ that is farther from the opticalaxis y than the emerging light ray E₃, E₄. Conversely, the farther thefirst light boundary 9 ₁ from the external limiting light ray I₄, i.e.the closer it is to the internal incident light ray I₃, the greater theincrease in the width of the dark zone or light transition T₁.

To summarize, the light boundary 9 ₁ must lie along the measurement axisx between the internal and external incident light rays I₃ and I₄, andit must be strictly between these two rays, i.e. it must not coincidewith either of them. The position of the second light boundary 9 ₂ isdefined in a manner analogous to the position of the first lightboundary 9 ₁.

Thus, the light boundaries 9 ₁ and 9 ₂ on either side of the opticalaxis y lie along the measurement axis x strictly between the internaland external incident light rays I₃ and I₄.

This ensures a perfect match between the position of the first lighttransition T₁ (or inside edge of the shadow) and the position of theinside face 4 of the hollow body. Naturally, and in similar manner,there is a perfect match between the position of the second lighttransition T₂ (or edge of the shadow) and the position of the insideface 4.

It can be seen from the above description that the distance along themeasurement axis x between the two light transitions T₁ and T₂ makes itpossible to measure the inside diameter of the hollow body along atleast one section of the body 2.

In a preferred variant embodiment in which the light source presents adetermined height Z_(L) along the vertical axis z, it is possible torecover the reflected and refracted emerging light rays so as to form animage of the hollow body 2 over a height, thus making it possible todetermine the distance between two light transitions along themeasurement axis x at different levels along the vertical axis z so asto measure the inside diameter (D₁, D₂, . . . , D_(j)) at variousheights of the hollow body 2 (FIG. 3).

According to an advantageous implementation characteristic, the methodof the invention consists in causing the hollow body 2 to revolve aboutits axis of revolution z, through at least half a revolution. For thispurpose, the hollow body 2 is driven in rotation by any appropriatemeans for rotating it about the axis of revolution z.

The method consists in processing the images acquired for differentangular positions in the rotation of the hollow item 2, with it beingpossible to measure its inside diameter in each of the images at one ormore heights.

Insofar as the inside diameter is measured at different heights of thehollow body 2, the method of the invention also makes it possible todetermine the profile of the inside face 4.

The inside diameter measurements are compared with reference values inorder to determine whether the hollow body is or is not defective. Whenthe profile of the inside face is determined, it is possible to envisagecomparing the measured inside profile of the inside face 4 with areference profile in order to determine whether the hollow body is or isnot defective.

In the embodiment shown in the drawings, the source 9 emits light allthe way from its center to its vertical light boundaries 9 ₁ and 9 ₂.

It should be observed that it is possible to make provision forilluminating the hollow item by using a light source 9 that extends outfrom the two light boundaries 9 ₁ and 9 ₂ on either side of the axis z,beyond the external incident light rays I₄. Using such a light sourcemakes it possible to obtain a gray scale image that is inverted relativeto the image J that is obtained using the light source shown in FIGS. 1and 2.

In the example shown, the light boundaries 9 ₁ and 9 ₂ extend along astraight direction parallel to the vertical axis z. Naturally, the lightsource 9 may present light boundaries that are not straight.Advantageously, the light boundaries 9 ₁ and 9 ₂ possess a profile or anoutline that is adapted to the profile of the inside diameter of thehollow body 2.

According to an advantageous embodiment characteristic, the light source9 includes an adjustment system for varying the distance along themeasurement axis x between the light boundaries 9 ₂ and 9 ₂. Such anadjustment system makes it possible to adapt to the size of the hollowitem 2 for inspection. To provide such an adjustment system, it ispossible to use a plurality of masks for the light source 9, or to use alight source 9 that is constituted by a series of light-emitting diodes(LEDs) with on/off control.

The invention is not limited to the embodiments described and shownsince various modifications can be applied thereto without going beyondits ambit.

1. A method of measuring the inside diameter of a hollow body ofrevolution (2) that is transparent or translucent and that is defined byan inside face (4) and an outside face (5), the body presenting an axisof revolution along a vertical axis (z), the method consisting inilluminating the hollow body (2) by means of a diffuse light source (9)and in recovering the light rays emerging from the hollow body (2) inorder to form at least one image, and being characterized by:illuminating the hollow body (2) on one side by means of a diffuse lightsource (9) so that the incident light rays (I_(i)) pass through thehollow body (2) along at least one cross-section perpendicular to theaxis of revolution and in which the inside diameter is to be measuredalong a measurement axis (x), the light source (9) presenting two lightboundaries (9 ₁, 9 ₂) spaced apart along the measurement axis (x) so asto create two light transitions (T₁, T₂) in the image that are spacedapart from each other and diametrically opposite about the vertical axis(z), corresponding to emerging light rays that propagate alongrespective lines tangential to the inside face (4) and perpendicular tothe diameter; from the side of the hollow body that is opposite from itsilluminated side, and by acting along an optical axis (y) that isperpendicular to the vertical axis (z) and perpendicular to themeasurement axis (x), recovering the light rays that are reflected andrefracted by the hollow body (2) so as to form at least one image (J) inwhich there appear at least the two light transitions (T₁, T₂); andprocessing the image (J) so as to determine the distance along themeasurement axis (x) between the two light transitions (T₁, T₂) in orderto determine a measurement for the inside diameter of the hollow body.2. A measurement method according to claim 1, characterized in that itconsists in illuminating a region of the hollow body (2) that extendsover a determined height along the vertical axis (z), in recovering thereflected and refracted emerging light rays so as to form an image ofthe hollow body over said height, and in determining the distance alongthe measurement axis (x) between two light transitions (T₁, T₂) atdifferent levels along the vertical axis (z) so as to determinemeasurements for the inside diameter at different heights of the hollowbody (2).
 3. A method according to claim 1, characterized in that itconsists in causing the hollow body (2) to rotate about the axis ofrevolution through at least part of a revolution and in processing theimages for different angular positions in rotation of the hollow item,with a measurement for the inside diameter at one or more heights beingtaken in each of those images.
 4. A method according to claim 2,characterized in that it consists in determining the profile of theinside face (4) from measurements of the inside diameter taken atdifferent heights.
 5. A method according to claim 1, characterized inthat it consists in comparing the measurements of the inside diameterwith reference values in order to determine whether the hollow body (2)is or is not defective.
 6. A method according to claim 1, characterizedin that it consists in illuminating the hollow body (2) by a lightsource (9) having light boundaries (9 ₁, 9 ₂) on either side of theoptical axis (y) that lie along the measurement axis (x) strictlybetween the position of an internal incident light ray (I₃) and theposition of an external incident light ray (I₄), the internal incidentlight ray (I₃) generating the emerging light ray (E₃) that is onlyrefracted on passing through the hollow body and that is situatedfarthest from the optical axis (y), while the external incident lightray (I₄) generates the emerging light ray (E₄) that is reflected by theinside face (4) of the hollow body and that is the closest to theoptical axis.
 7. A method according to claim 6, characterized in that itconsists in illuminating the hollow body (2) by a light source (9) thatemits light from its center and up to its light boundaries (9 ₁, 9 ₂).8. A method according to claim 6, characterized in that it consists inilluminating the hollow body (2) by a light source (9) that extends fromthe two light boundaries (9 ₁, 9 ₂) on either side of the axis (x) andbeyond the external incident light ray (I₄).
 9. An appliance formeasuring the inside diameter of a hollow body of revolution (2) that istransparent or translucent and that is defined by an inside face (4) andan outside face (5), the body presenting an axis of revolution along avertical axis (z), the appliance comprising a light source (9) emittinglight rays illuminating the hollow body (2) and a recovery system (11)for recovering light rays emerging from the hollow body (2) in order toform at least one image, and an image acquisition and processor unit(15), the appliance being characterized in that it comprises: a diffuseand extensive light source (9) arranged so that the incident light rayspass through the hollow body (2) from one side and along at least onecross-section perpendicular to the axis of revolution and in which theinside diameter is to be measured along a measurement axis (x), thelight source (9) presenting two light boundaries (9 ₁, 9 ₂) spaced apartalong the measurement axis (x) so as to create two light transitions(T₁, T₂) in the image, which transitions are spaced apart from eachother and diametrically opposite about the vertical axis (z),corresponding to emerging light rays that propagate along respectivelines tangential to the inside face (4) and perpendicular to thediameter; on the side of the hollow item opposite from its sideilluminated by the source, a recovery system (11) for acting along anoptical axis (y) that is perpendicular to the vertical axis (z) andperpendicular to the measurement axis (x) to recover emerging light rays(E_(i)) as reflected and refracted by the hollow item, the systemforming at least one image (J) in which there appear at least two lighttransitions (T₁, T₂) that are spaced apart from each other anddiametrically opposite relative to the vertical axis (z); and an imageacquisition and processor unit (15) formed by the recovery system (11)in order to determine the distance along the measurement axis (x)between the two light transitions (T₁, T₂) in order to determine ameasurement for the inside diameter of the hollow body.
 10. An applianceaccording to claim 9, characterized in that the diffuse and extensivelight source (9) possesses a determined height (Z_(L)) along thevertical axis (z) for illuminating a vertical region of the hollow body,the recovery system (11) recovers the emerging light rays reflected andrefracted by the hollow body in a vertical region (Z_(L)) in order toform a corresponding image, and the image processor unit determines thedistance between two light transitions (T₁, T₂) along the measurementaxis (x) at different levels along the vertical axis (z) in order todetermine measurements for the inside diameter at different heights ofthe hollow body (2).
 11. An appliance according to claim 9,characterized in that it includes a system for causing the hollow body(2) to rotate about the axis of revolution (3).
 12. An applianceaccording to claim 9, characterized in that the light boundaries (9 ₁, 9₂) of the light source (9) on either side of the optical axis (y) liealong the measurement axis (x) strictly between the position of aninternal incident light ray (I₃) and the position of an externalincident light ray (I₄), the internal incident light ray (I₃) generatingthe emerging light ray (E₃) that is only refracted on passing throughthe hollow body (2) and that is situated farthest from the optical axis(y), while the external incident light ray (I₄) generates the emerginglight ray (E₄) that is reflected by the inside face (4) of the hollowbody (2) and that is the closest to the optical axis (y).
 13. Anappliance according to claim 12, characterized in that the source (9) isluminous from its center out to its light boundaries (9 ₁, 9 ₂) formingits vertical edges.
 14. An appliance according to claim 9, characterizedin that the light boundaries (9 ₁, 9 ₂) of the light source areoptionally rectilinear with a profile that is adapted to the profile ofthe inside diameter of the hollow body (2).
 15. An appliance accordingto claim 9, characterized in that the light source (9) includes anadjustment system serving to vary the distance between the lightboundaries (9 ₁, 9 ₂).
 16. An appliance according to claim 15,characterized in that, as its adjustment system, it includes one or moremasks for the light source (9), or a light source (9) made using aseries of light-emitting diodes with on/off control.
 17. An applianceaccording to claim 9, characterized in that the recovery system (11)comprises a camera (12) having a telecentric lens (13) so that thecollected emerging light rays (E_(i)) are parallel to the optical axis(y) of the recovery system (11).